After a well has been produced and fluid production is obtained from one or more zones of the well, it is necessary to measure the rate of flow in the well. When it is a single formation producing into the well, the rate of flow at the formation is the same as the rate of flow from the wellhead. Thus, the rate of production from a formation that several thousand feet deep can be quickly known by measuring the rate of flow from the wellhead. This simple case however does not apply where there is more than one producing formation. It is possible that both formations will produce. It is also possible that one of the formations will later fail to produce and will draw off production. Thus, the rate of production at the two formations can vary widely even to the point where production is actually lost from one formation into another. Measurement at the well head may yield the net production but it does not yield the individual formation production rates.
Production from a formation is an important parameter in well control. For instance, different types production equipment can be installed. Different production enhancement techniques can be used including various fracture techniques and the like. Such fracture techniques and production enhancement techniques are materially assisted if the rate of production from a formation is known, or indeed the fact that loss into a particular formation has occurred. The present apparatus is particularly useful in determining rate of production. It is particularly adapted to be used in a cased well which intersects one or more horizons having perforations through the casing into the horizons.
In view of the fact that the well is cased, the cross sectional flow area along the well is then known. The present apparatus is an injector which delivers a controlled flow of a tracer fluid. The tracer fluid is injected into the cased well, and its passage is noted further up the well. Tracer passage is detected by means of a suitable radioactivity detector. In this measurement, a geiger tube or a scintillation detector measuring device can be used. If the time at which the tracer fluid is injected into the fluid flow in the cased well is known, then the fluid is measured at the moment it passes the detector. This elapsed time for travel over a known distance can be used in conjunction with knowledge of the dimensions of the cased well to provide an indication of flow rate.
It will be appreciated that the handling of the tracer fluid is a critical matter. So to speak, the tracer fluid should be delivered only on command and such delivery should be controllable. That is, the tracer element delivery should be carefully timed for onset and volume. The present apparatus is a device which enables careful delivery and controlled volumetric flow of tracer. It is particularly adapted to be incorporated in a sonde for delivery of the tracer into the fluid flow in the well so that production can be measured by observation of the passage of the tracer element.
The present apparatus is an injector incorporated in a sonde. It fits in an elongate tubular structure. It has a separate, removable cartridge which is filled with the radioactive fluid. The cartridge is a separate unit which can be plugged into the housing in a suitable receptacle. Since it is a separate cartridge, this assures safe handling, both before and after use, thereby assuring that the radioactive material in the housing does not escape. This avoids contamination problems. Moreover, this technique of installation of the cartridge in the injector permits selective change of injector cartridge and also selective change of tracer. The present apparatus thus incorporates a separate cartridge, a check valve system, a pump system operated by a controllable solenoid drive mechanism and an outlet through a sized orifice. This assures controllable injection of the tracer into the well fluid.
While the foregoing touches on the apparatus which is involved in this disclosure and also discusses the method of use, more details will be observed on a review of the detailed description found below.